Project Background/Rationale. Obstructive sleep apnea/hypopnea (OSAH) is a common chronic disease that is associated with daytime sleepiness, impaired health-related quality of life (QOL), and increased risk of hypertension and cardiovascular disease. The most common treatment is continuous positive airway pressure (CPAP), although adherence to CPAP is poor in more than one-third of patients. Weight loss can clearly lessen the severity of OSAH, but although short-term dietary weight loss can often be achieved it is difficult to maintain. Regular aerobic exercise is associated with a lower prevalence of OSAH in observational studies after adjustment for body habitus, and in two small clinical trials moderate exercise was associated with a substantial decrease in OSAH severity despite little or no weight loss. Demonstrating that dietary weight loss and moderate physical activity, promoted via easily administered telehealth applications in the home setting, independently improve OSAH severity will have a major impact on the therapeutic approach to OSAH, a disease that is highly prevalent in the VA population. Project Objectives. We hypothesize that both moderate-intensity physical activity and dietary weight loss will independently reduce OSAH severity and daytime sleepiness and improve OSAH-related QOL. We further hypothesize that the effects of diet and physical activity will be mediated by changes in adiposity, particularly changes in regional fat distribution and upper airway dimensions that may be independent of weight loss. The specific objectives are to determine the effects on OSAH severity, daytime sleepiness, and QOL of (1) six months of moderate-intensity physical activity promotion and (2) six months of dietary weight loss promotion. Furthermore, we will determine the effect of the physical activity promotion intervention on physical activity and the effect of the weight loss promotion intervention on BMI. A secondary objective is to determine the impact of these interventions on regional fat distribution and upper airway dimensions, which are proposed mediators of the effect of the interventions on OSAH. Project Methods. The proposed study is a randomized clinical trial using a 2 x 2 factorial design to test the independent effects of the physical activity and diet interventions, with an attention control intervention for subjects not assigned to either active intervention. Subjects will be 180 male and female veterans age 18-80 years, with a BMI 25-40 kg/m2, with a physician diagnosis of OSAH and apnea-hypopnea index (AHI) >10/hr who are non-adherent to CPAP therapy. The physical activity intervention is a 6-month progressive walking regimen with heart rate monitoring and real-time feedback using Windows Mobile computer technology, permitting self-administration in the home setting. The dietary weight loss intervention is a 6-month program administered in the home setting via a handheld mobile device based on the VA's MOVE! program. Outcomes include the AHI derived from polysomnography, Epworth Sleepiness Scale score, Functional Outcomes of Sleep Questionnaire, BMI, physical activity, ultrasound measures of visceral and subcutaneous abdominal fat, and upper airway dimensions by acoustic pharyngometry.